Construction for an Implantable Medical Device Having a Battery Affixed to the Case

ABSTRACT

Designs and methods of construction for an implantable medical device employ an internal support structure. The single-piece support structure holds various electronic components such as a communication coil and a circuit board, and further is affixed to a battery, thus providing a subassembly that is mechanically robust. The support structure further provides electrical isolation between these and other components. A method of construction allows for the subassembly to be adhered to a case of the implantable medical device at the battery, and possibly also at the support structure. The battery includes an insulating cover having holes. An adhesive is used consistent with the location of the holes to affix the battery to the case without electrically shorting the battery to the case.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Non-Provisional patent application Ser.No. 14/469,872, filed Aug. 27, 2014, which is a Non-Provisional of U.S.Provisional Patent Application Ser. No. 61/874,197, filed Sep. 5, 2013.Priority is claimed to these applications, and they are incorporatedherein by reference in their entireties.

This application is related to an application entitled “Construction foran Implantable Medical Device Employing an Internal Support Structure,”Ser. No. 61/874,194, filed Sep. 5, 2013, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to implantable medical devices, and moreparticularly to an improved design and method of construction for animplantable medical device.

BACKGROUND

Implantable stimulation devices deliver electrical stimuli to nerves andtissues for the therapy of various biological disorders, such aspacemakers to treat cardiac arrhythmia, defibrillators to treat cardiacfibrillation, cochlear stimulators to treat deafness, retinalstimulators to treat blindness, muscle stimulators to producecoordinated limb movement, spinal cord stimulators to treat chronicpain, cortical and deep brain stimulators to treat motor andpsychological disorders, and other neural stimulators to treat urinaryincontinence, sleep apnea, shoulder subluxation, etc. The descriptionthat follows will generally focus on the use of the invention within aSpinal Cord Stimulation (SCS) system, such as that disclosed in U.S.Pat. No. 6,516,227. However, the present invention may findapplicability with any implantable medical device or in any implantablemedical device system.

A SCS system typically includes an Implantable Pulse Generator (IPG)which has a biocompatible device case formed of a conductive materialsuch as titanium, for example. The case typically holds the circuitry ofthe IPG and a battery to provide power to the circuitry. Depending onthe particular needs and circumstances of the patient who will be usingthe IPG, the battery can be either rechargeable or a non-rechargeableprimary battery.

Although many IPGs use rechargeable batteries, there are situations inwhich use of a primary battery may be advantageous. A primary battery isone in which the electrochemical reaction is not reversible by passing acharging current therethrough, thus rendering the batterynon-rechargeable. Primary batteries use up the materials in one or bothof their electrodes and thus have a limited life span, but they aretypically cheaper than rechargeable batteries, and may not suffer fromthe same reliability concerns. As such, the use of primary batteries ina medical implantable device is preferred when appropriate, for example,when the expected life of the primary battery would be expected toexceed the patient's life expectancy, or in situations where patientswith physical or mental limitations would have difficulty charging thebattery. Use of a primary battery in an IPG, however, creates achallenge in the design and construction of the IPG, as a primarybattery is generally larger in size than a rechargeable one, and it isnot optimal to increase the size of the IPG.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an improved Implantable Pulse Generator (IPG) and themanner in which electrode leads are affixed to the IPG.

FIG. 2 shows bottom and top views of the improved IPG with its caseremoved.

FIG. 3 shows bottom and top perspective views of the improved IPG withits case removed.

FIGS. 4A and 4B respectively show bottom and top perspective explodedviews of the components of the improved IPG.

FIG. 5 shows bottom and top perspective views of a support structureused in the improved IPG.

FIGS. 6A and 6B respectively show top and cross-sectional views of asubassembly of the improved IPG at one stage of its construction.

FIG. 7 shows positioning of a battery cover over the battery in thesubassembly at another stage of construction.

FIG. 8 shows placement of glue drops on an IPG case portioncorresponding to locations of glue holes in the subassembly at anotherstage of construction.

FIG. 9 shows affixing the subassembly to the case portion using the gluedrops, and encompassing the subassembly in the IPG case, at anotherstage of construction.

FIG. 10A shows cross sections of the completed IPG, and FIG. 10B showsthe manner in which the glue drops adhere the battery and the supportstructure to the case.

DETAILED DESCRIPTION

This disclosure provides an improved design and method of constructionfor an implantable medical device, and in particular an implantablemedical device having a larger primary battery. However, the design andmethod of construction are not limited to implantable medical devicesthat use primary batteries, and can be used with rechargeable-batteryIPGs as well. This improved design is easy to construct, mechanicallyrobust, and uses few parts.

FIG. 1 shows a SCS system having an IPG 10. The IPG 10 includes abiocompatible device case 30 that holds the circuitry and battery 34(FIG. 2) necessary for the IPG to function. The IPG 10 is coupled toelectrodes 16 via one or more electrode leads 14 that form an electrodearray 12. The electrodes 16 are carried on a flexible body 18, whichalso houses the individual signal wires 20 coupled to each electrode.The signal wires 20 are connected to the IPG 10 at one or more leadconnectors 24 fixed in a header 28, which can comprise an epoxy forexample. In the illustrated embodiment, there are sixteen electrodessplit between two leads 14, although the number of leads and electrodesis application specific and therefore can vary. In a SCS application,electrode leads 14 are typically implanted on the right and left side ofthe dura within the patient's spinal cord. The proximal ends 22 of theleads 14 are then tunneled through the patient's flesh to a distantlocation, such as the buttocks, where the IPG case 30 is implanted, atwhich point they are coupled to the lead connector(s) 24.

FIGS. 2, 3, and 4A and 4B show various perspectives of the bottom side(the side proximate a communication coil 40) and top side (the sideproximate to a printed circuit board (PCB) 42) of the improved IPG 10.The case 30, which in the depicted example is formed as two caseportions 30 a and 30 b, is removed in FIGS. 2 and 3 so that certaininternal components can be seen, some of which are introduced now priorto discussion of the construction of the IPG 10.

As shown, the majority of the room inside the case 30 is taken up by abattery 34 which, in this example, is a permanent,non-wirelessly-rechargeable battery. The remainder of the room in thecase 30 is largely taken up by a support structure 38, communicationantenna 40, which is this example comprises a coil, and a PCB 42. Thecommunication coil 40 enables communication between the IPG 10 and adevice external to the patient (not shown), thus allowing bidirectionalcommunication to occur by magnetic induction. The PCB 42 includescircuitry configured to implement the functionality of the implantablemedical device. The lead connectors 24 are coupled to the PCB 42 byfeedthrough pins 48, which proceed through a feedthrough 32 that isultimately welded to the case 30 prior to securing the header 28 to theIPG 10, as explained below. Suture holes 41 and 43 in the header areused to suture the IPG to a patient's body during an operation.

Construction of the IPG 10 begins with the discussion of the supportstructure 38, which is shown in bottom and top perspective views in FIG.5. The support structure 38 provides many benefits to the IPG 10. Thesupport structure 38 comprises a single piece for receiving, holding,and protecting both the coil 40 and PCB 42. The coil 40, PCB 42, andbattery 34 are affixed to the support structure 38, which integrates theconnections of these components and results in a mechanically-robust IPGsubassembly 92 (FIG. 6A) resistant to shock and vibration. Supportstructure 38 also provides electrical isolation between the coil 40 andthe PCB 42 (excepting the coil pins 44 explained below); between thebattery 34 (particularly, the positive terminal 46 a of the battery 34)and the coil 40, PCB 42, or feedthrough pins 48; and between thefeedthrough pins 48 and the coil 40, and thus prevents unwanted shortingof these components.

The support structure 38 also provides one or more case contact surfaces76 with at least one glue hole 60 to allow the support structure 38, andhence the already-robust IPG subassembly 92, to be adhered to the case30. The IPG subassembly 92 may additionally be adhered to the case 30 bythe battery 34, as discussed below.

The support structure 38 includes a recess 74 into which the coil 40 isaffixed. The coil 40 was earlier wound around a bobbin (not shown). Thecoil 40 is preferably recessed below the case contact surfaces 76 of thesupport structure 38 to protect it and to offset the coil 40 from thecase 30 once the IPG 10 is constructed, as discussed further below. Theends of the coil 40 are soldered to coil pins 44 on the bottom side ofthe support structure 38, which coil pins 44 pass through the supportstructure 38 and are preferably molded into the support structure 38during its construction. Later in the construction process, the other(top) side of coil pins 44 will be soldered to the PCB 42 on the topside of the support structure 38 to electrically couple the coil to theelectronics on the PCB 42 such as modulation and/or demodulationcircuitry. Coil 40 may be further affixed within the recess 74 using anepoxy or other adhesive. Coil 40 may be covered with tape 72 as shown toelectrically isolate the coil 40 from the feedthrough pins 48, whichlater during construction will be located within a gap 84 in a sidewall80 of the support structure 38.

The support structure 38 is preferably made of a material with highmelting temperature able to withstand soldering of the coil pins 44 tothe coil 40 and to other structures as subsequently explained. Thematerial for the support structure 38 is also preferably mechanicallyrigid to provide mechanical robustness, and should have a low moisturecontent consistent with its use with electrical components and in animplantable medical device. In one embodiment, the material comprises aLiquid Crystal Polymer (LCP).

Several features of the support structure 38 that provide some of thebenefits discussed earlier are noticeable in FIG. 5. For example, thetop of the support structure 38 includes support ribs 86 and mountingpins 88 that help to support and position the PCB 42 that will beaffixed to the support structure 38 later during construction. Thesupport structure 38 also includes cavities 78, which provides space fortaller components on the PCB 42. The cavities 78 also help to define therecess 74 for the coil 40, and provide two case contact surfaces 76 withglue holes 60 on the bottom side of the support structure 38, which asalready noted is useful in adhering the support structure to the IPG'scase 30. The sidewall 80 of the support structure 38 again helps todefine the recess 74 and isolate the coil 40, and additionally comprisesa portion 82 to which the battery 34 will be affixed, as explainedlater. An isolation structure 90 and gap 83 in the sidewall willaccommodate the positive and negative terminals 46 a and 46 b of thebattery 34 later during construction. Jig mounting holes 106 can also beseen on the bottom of the support structure 38, whose function is laterexplained.

After formation of the support structure 38, various pieces of the IPG10—for example, the support structure 38, the PCB 42, the battery 34 anda lead connector subassembly 95 (explained below)—can be electricallyand mechanically attached to form an IPG subassembly 92, as shown in topand cross-sectional views of FIGS. 6A and 6B.

Construction begins by adhering double sided tape 58 to the face 57 ofthe battery 34 that contains the battery terminals (FIGS. 4A and 4B).The other side of the double sided tape 58 is adhered to the sidewallportion 82 of the support structure 38. As noted earlier, the supportstructure 38 preferably already contains the coil 40 pre-soldered to thecoil pins 44, but the coil could also be affixed to the supportstructure at this time or later during construction, such as whensoldering of components to the PCB 42 subsequently occurs. Because thecase contact surfaces 76 on the bottom of the support structure 38 andthe bottom surface of the battery 34 are preferably planar, supportstructure 38 and battery 34 can be affixed with the double sided tape 58by sliding them together on a flat surface. It is not strictly necessaryto use double sided tape 58 to affix the battery 34 to the supportstructure 38, and glue or other adhesives could be used as well.

The terminals 46 a and 46 b of the battery 34 are bent at 90 degreesrelative to the flat battery terminal surface of the battery 34 and soare now pointing upward, as best shown in the top view of FIG. 5. Noticein FIG. 5 that the negative terminal 46 b passes through the gap 83 inthe sidewall 80 of the support structure 38, and that the positiveterminal 46 a of the battery 34 is at least partially surrounded by theisolation structure 90 formed in the support structure 38. As such, thesupport structure 38, in addition to other functions, serves to isolatethe positive battery terminal 46 a from shorting to the negative batteryterminal 46 b and other components in the IPG 10, such as the coil 40and the PCB 42. Isolation structure 90 could be made in differingmanners. The negative battery terminal 46 b could also be isolated usingan isolation structure 90.

Next, the combined support structure 38 and battery 34 is placed in anassembly jig 94 as shown in FIG. 6B, which has recesses conforming tothe shape of these pieces it receives to align and hold them duringconstruction. As shown, the jig 94 can have mounts 98 designed to matewith the jig mounting holes 106 on the bottom side of the supportstructure 38 to securely hold the combined support structure 38 andbattery 34 in the jig 94. Other means of support with the jig 94 couldbe used as well.

Next, a lead connector subassembly 95 is positioned within the jig 94.The lead connector subassembly 95 includes the lead connectors 24, theelectrode contacts 26, a carrier 64 (used to house and support theelectrode contacts 26; see FIGS. 4A and 4B), the feedthrough pins 48,and the feedthrough 32, and may be pre-formed prior to this step inconstruction. For example, lead connector subassembly 95 can be formedby slipping the feedthrough pins 48 through the feedthrough 32,soldering one end of the feedthrough pins 48 to appropriate electrodecontacts 26 in the lead connectors 24, and (if necessary) soldering thefeedthrough pins 48 in the feedthrough 32 in a hermetic manner. Noticethat the free end of the feedthrough pins 48 are bent at 90 degreesrelative to the feedthrough 32 (as best seen in FIG. 4B), and so whenplaced in the jig 94 are now pointing upward. Notice also that thefeedthrough pins 48 will be positioned in the gap 84 in the sidewall 80of the support structure 38 (FIG. 5), as discussed earlier.

Next, the PCB 42—preferably pre-fabricated with its electricalcomponents—is affixed to the top side of the support structure 38. Inthis regard, PCB 42 includes coil solder pin holes 50, battery terminalsolder holes 52, feedthrough pin solder holes 54, and support structuremounting holes 56, which are respectively slipped over and brought intocontact with the upward-pointing coil pins 44, feedthrough pins 48,battery terminals 46 a and 46 b, and mounting pins 88 of the supportstructure 38. Once the PCB 42 is slid over these structures, it comes torest on the support ribs 86 (FIG. 5), which provides suitable mechanicalsupport to keep the PCB 42 from flexing. The coil pins 44, feedthroughpins 48, battery terminals 46 a and 46 b are then soldered to the coilsolder pin holes 50, feedthrough pin solder holes 54, and batteryterminal solder holes 52 respectively to electrically couple them to thePCB 42. The combined effect of the support ribs 86, mounting pins 88,and the soldered connections yields a PCB 42 that is firmly affixed toand protected by the support structure 38 to complete the IPGsubassembly 92. Although not shown, the PCB 42 can also be recessed inthe support structure 38 to further electrically isolate it form otherstructures and for further mechanical protection.

Once IPG subassembly 92 has been constructed, it is removed from the jig94, and a battery cover 68 is slipped over the battery 34, as shown inFIG. 7. The battery cover 68 typical comprises a thin plastic sleeve,and is used to electrically isolate the battery 34's case from the case30 of the IPG 10, which may be at different potentials. The batterycover 68 includes at least one battery cover glue hole 70 through whichthe battery 34 can be adhered to the case 30 while still providing thedesired electrical isolation.

The battery cover 68 may completely surround the battery 34, but asshown it only partially surrounds the battery 34, covering all surfacesof the battery 34 except the battery terminal face 57. However, thebattery cover 68 is not limited, and other insulators may be used aswell. For example, an insulative coating might be provided on the caseof the battery 34, masked as necessary to form the glue holes 70 in thecoating. Alternatively an insulating layer or sheet may be used thatintervenes between the battery 34's case and the IPG case 30 where theycome into contact or are close to doing so. This alternative of use of asingle insulting layer or sheet might be a good option for use in theIPG 10, because as discussed further below with respect to FIGS. 10A and10B, the battery 34 is affixed to the bottom side of the case 30 and anair gap “x” exists between the battery and the top side of the case, andthus an insulator may not be necessary on this side as the battery 34and the case 30 are less likely to short by virtue of this air gap. Thebattery cover 68 or other insulator may also cover other portions of theIPG subassembly 92, such as the support structure to which the coil 40and the PCB 42 are affixed to also prevent these structures fromshorting to the case 30.

As shown in FIG. 8, glue drops 96 are placed at multiple locationsinside the bottom case portion 30 b corresponding with the position ofthe support glue holes 60 in the support structure 38 and battery coverglue holes 70 in the battery cover 68. The IPG subassembly 92 ispositioned in the bottom case portion 30 b, as shown in FIG. 9, whichcauses the glue drops 96 to penetrate through the glue holes 70 in thebattery cover 68 to come in contact with the battery 34, and through theglue holes 60 in the support structure 38, as further discussed belowwith respect to FIG. 10B. Alternatively, glue drops 96 could be placedon the IPG subassembly 92 at the holes 60 and 70, which is thenpositioned in the bottom case portion 30 b. Glue drops 96 suitable forthis application include NuSil™ Med3-4213 silicone, but other types ofglues or other adhesives may be used as well. For example, double sidedtape could be used in place of glue drops 96. The adhesive used at thisstep could comprise the same adhesive (58) used to affix the battery 34to the support structure 38.

As further shown in FIG. 9, after the IPG subassembly 92 is affixed tothe bottom case portion 30 b via the glue drops 92, the top case portion30 a is positioned to surround at least part of the IPG assembly 92 (butnot lead connector subassembly 95) in the case portions 30 a and 30 b,and to meet the feedthrough 32 at cutouts 62 a and 62 b (FIGS. 4A and4B) in the case portions 30 a and 30 b. (Note that an applicator 66(FIGS. 4A and 4B) is used as an aid to properly align the case). Thecase portions 30 a and 30 b are then preferably laser welded togetherand laser welded to the feedthrough 32, although other sealing methodscould be used, such as brazing, or the use of hermitic glues or otheradhesives.

Top and bottom case portions 30 a and 30 b with parallel top and bottomsides are not required, and instead the case 30 could comprise a uniformstructure generally resembling a “cup” into which the subassembly 92 isplaced and affixed. Such a cup-shaped case may also have parallel topand bottom sides. A cap, which may include the feedthrough 32, can thenbe welded to the open end of the cup.

Thereafter, the epoxy header 28 (FIG. 1) is affixed to the case 30around the lead connectors 24 and the feedthrough 32 to from a hermeticseal in standard fashions, at which point construction of the IPG 10 iscomplete.

FIG. 10A shows a cross section of the fully constructed IPG 10, whichallows certain aspects and benefits of the design of the IPG to beappreciated. The bottom side of the battery 34 and the case contactsurfaces 76 of the support structure 38 are planar and both are affixedto the bottom case portion 30 b as is preferable to add mechanicalrobustness. However, this is not strictly necessary, and instead onlyone of the battery 34 and support structure 38 can be so affixed.Likewise, it is also not necessary that the bottom sides of the battery34 and the case contact surfaces 76 of the support structure 38 areplanar. Note the case contact surfaces 76 of the support structure 38offset the coil 40 from the bottom case portion 30 b to prevent shortcircuiting of the coil.

As shown, the relatively-large primary battery 34 occupies first area 11a in the case 30, while the support structure 38, coil 40, and PCB 42occupy a second smaller area 11 b in the case 30. The areas 11 a and 11b preferably do not overlap. This is advantageous because the supportstructure 38, coil 40, and PCB 42 do not require the battery 34 to bethinned, as would occur if these structures overlapped. Because thebattery 34 is not constrained by the thickness of these structures, thethickness of the battery 34 is allowed to substantially equal thethickness of the case 30 (e.g., within 15%). Coil 40 and PCB 42 areparallel and overlap each other in the second area 11 b, and areparallel to the top and bottom sides of the case 30, and perpendicularto the battery terminal face 57 of the battery 34 and feedthrough 32. Asshown, the support structure 38, coil 40, and PCB 42 can all be made tofit equal to or less than the thickness of the battery 34, which againdoes not constrain the thickness that the battery 34 can have inside thecase 30. Although, this is not strictly necessary.

A small air gap “x” intervenes between the top side of the battery 34and support structure 38 and the top case portion 30 a, which is usefulto protecting the battery 34 from heat during welding of the two caseportions 30 a and 30 b. As a further protection against this heat, aback-up band 36 (not shown in FIG. 3) can be provided around theperiphery of the IPG assembly 92, as best shown in FIG. 9. However, useof an air gap x is not strictly necessary. For example, the battery 34could be affixed (e.g., glued) to both the top and bottom case portions30 a and 30 b to leave no air gap, which would require battery coverglue holes 70 on both sides of the battery cover 68.

FIG. 10B is magnified illustration of the glue holes 70 in the batterycover 68 and the glue holes 60 in the case contact surfaces 76.Preferably enough glue 96 is provided to penetrate completely throughthe glue holes 60 to the other side of the support structure 38, thuscreating a mushroom-shaped when dried, to anchor the support structure38 to the bottom side case portion 30 b. This preference though is notstrictly necessary, and indeed the case contacts surfaces 76 can beglued or affixed to the bottom case portion 30 b even if holes 60 arenot present.

FIG. 10B also illustrates how glue 96 penetrates the glue holes 70 inthe battery cover 68 to adhere the battery 34 to the bottom case portion30 b. Glue holes 70 are particularly advantageous in this case, becausethe material of the battery cover 68 is generally not suitable foradhesion. Because the material of the glue 96 is insulative, the battery34 is affixed to the case 30 (despite the intervening battery cover 68)but is still electrically insulated therefrom, which as noted earlier isdesired because they may be at different potentials.

It should be noted that the above construction steps are merely examplesof how the IPG 10 as designed can be constructed, and other manners arealso possible. For example, construction steps can occur in differentorders, or involve different sub-steps or the consolidation of steps.

While the disclosed IPG design and method of construction were inspiredby the use of larger primary batteries, the disclosed design and methodscould also be used for an IPG having a rechargeable battery. In such acase, the IPG might have an additional antenna (not shown), such asanother coil to wirelessly receive a charging field that is rectified tocharge the battery. Such additional charging coil, like communicationcoil 40, could also be affixed to the disclosed support structure 38.Alternatively, the disclosed coil 40 could comprise a combinedcommunication/charging coil capable of performing both communication andcharging functions.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. An implantable medical device, comprising: acase; circuitry within the case configured to implement thefunctionality of the implantable medical device; a battery within thecase electrically coupled to the circuitry; and a battery coverconfigured to electrically isolate the battery from the case, whereinthe battery cover surrounds all surfaces of the battery other than thebattery's terminal face.
 2. The device of claim 1, wherein the batterycomprises a primary battery.
 3. The device of claim 1, wherein thebattery cover comprises a plastic sleeve configured to slip over thebattery.
 4. The device of claim 1, wherein the battery cover is aninsulative coating provided on the battery.
 5. The device of claim 4,wherein there are one or more breaks in the insulative coating at whichthe battery surface is exposed.
 6. The device of claim 5, wherein thebattery is affixed to the case by an adhesive applied at the one or morebreaks. The device of claim 1, wherein the battery cover comprises atleast one hole.
 8. The device of claim 7, wherein the battery is affixedto the case by an adhesive through the at least one hole.
 9. The deviceof claim 8, wherein the adhesive comprises glue.
 10. The device of claim8, wherein the adhesive comprises a silicone adhesive.
 11. The device ofclaim 8, wherein the adhesive electrically isolates the battery from thecase at the at least one hole.
 12. The device of claim 8, wherein thecase comprises a first portion and a second portion and wherein thebattery is affixed to only the first portion.
 13. The device of claim12, wherein there is an air gap between the battery and the secondportion.
 14. An implantable medical device, comprising: a case;circuitry within the case configured to implement the functionality ofthe implantable medical device; a battery within the case electricallycoupled to the circuitry; an insulating sleeve that surrounds at least aportion of the battery, wherein the insulating sleeve is a plasticsleeve that has at least one hole and is configured to slip over thebattery; and an adhesive that affixes the battery to the case throughthe at least one hole, wherein the battery is electrically isolated fromthe case by the insulating sleeve and the adhesive.
 15. The device ofclaim 14, wherein the battery comprises a primary battery.
 16. Thedevice of claim 14, wherein the adhesive comprises glue.
 17. The deviceof claim 14, wherein the adhesive comprises double-sided tape.
 18. Thedevice of claim 14, further comprising a support structure within thecase, wherein the battery is affixed to the support structure.
 19. Thedevice of claim 18, wherein the circuitry is affixed to the supportstructure.
 20. The device of claim 19, further comprising an antennarecessed within the support structure.